The present invention relates generally to heat-transfer label assemblies and more particularly to a novel heat-transfer label assembly and to a method of using the same.
Heat-transfer labels are implements commonly used to decorate and/or to label commercial articles, such as, and without limitation to, containers for beverages (including alcoholic beverages, such as beer), essential oils, detergents, adverse chemicals, as well as health and beauty aids. As can readily be appreciated, heat-transfer labels are desirably resistant to abrasion and chemical effects in order to avoid a loss of label information and desirably possess good adhesion to the articles to which they are affixed. Heat-transfer labels are typically constructed as part of a heat-transfer label assembly, with one or more heat-transfer labels printed on a removable carrier web.
One of the earliest types of heat-transfer label assemblies is described in U.S. Pat. No. 3,616,015, inventor Kingston, which issued October, 1971, and which is incorporated herein by reference. In the aforementioned patent, there is disclosed a heat-transfer label assembly adapted for labeling plastic objects, the heat-transfer label assembly comprising a paper sheet or web, a wax release layer affixed to the paper sheet, and an ink design layer printed on the wax release layer. In the heat-transfer labeling process, the label-carrying web is subjected to heat, and the label is pressed onto a plastic article with the ink design layer making direct contact with the plastic article. As the paper sheet is subjected to heat, the wax layer begins to melt. This enables the paper sheet to be released from the ink design layer, with a portion of the wax layer being transferred with the ink design layer onto the plastic article and with a portion of the wax layer remaining with the paper sheet. After transfer of the design to the plastic article, the paper sheet is immediately removed, leaving the design firmly affixed to the plastic article and the wax transferred therewith exposed to the environment. The wax layer is thus intended to serve two purposes: (1) to provide release of the ink design from the web upon application of heat to the web and (2) to form a protective layer over the transferred ink design. After transfer of the label to the article, the transferred wax release layer is typically subjected to a post-flaming or post-heating technique which involves subjecting the transferred wax release layer to jets of high temperature gas either as direct gas flames or as hot air jets to produce wax surface temperatures of about 300° F. to 400° F. for a period of time sufficient to remelt the transferred wax. This remelting of the transferred wax is performed to enhance the optical clarity of the wax protective layer (thereby enabling the ink design layer therebeneath to be better observed) and to enhance the protective properties of the transferred wax release.
Unfortunately, despite the aforementioned post-flaming step, the transferred wax layer is often perceptible on clear and/or dark-colored objects.
Consequently, a great deal of effort has been expended in replacing or obviating the need for a wax release layer. One type of heat-transfer label assembly that does not include a wax release layer is exemplified by U.S. Pat. No. 4,935,300, inventors Parker et al., which issued Jun. 19, 1990, and which is incorporated herein by reference. In the aforementioned Parker patent, the label assembly, which is said to be particularly well-suited for use on high density polyethylene, polypropylene, polystyrene, polyvinylchloride and polyethylene terephthalate surfaces or containers, comprises a paper carrier web which is overcoated with a layer of thermoplastic polyethylene. A protective lacquer layer comprising a polyester resin and a relatively small amount of a nondrying oil is printed onto the polyethylene layer. An ink design layer comprising a resinous binder base selected from the group consisting of polyvinylchloride, acrylics, polyamides and nitrocellulose is then printed onto the protective lacquer layer. A heat-activatable adhesive layer comprising a thermoplastic polyamide adhesive is then printed onto the ink design layer.
Although the above-described Parker label assembly substantially reduces the wax-related effects discussed previously, said label assembly does not quite possess the same release characteristics of heat-transfer label assemblies containing a wax release layer. In fact, when put to commercial use, the polyethylene release layer of the Parker label assembly was found to become adhesive when subjected to the types of elevated temperatures typically encountered during label transfer. Accordingly, another type of heat-transfer label assembly differs from the Parker heat-transfer label assembly in that a very thin layer or “skim coat” of carnauba wax is interposed between the polyethylene release layer and the protective lacquer layer to improve the release of the protective lacquer from the polyethylene-coated carrier web. The thickness of the skim coat corresponds to approximately 0.1-0.4 lbs. of the wax spread onto about 3000 square feet of the polyethylene release layer. The aforementioned “skim coat-containing” heat-transfer label assembly also differs from the Parker label assembly in that the heat-activatable adhesive of the “skim coat” label assembly is printed over the entirety of the ink and protective lacquer layers, with the peripheral edges of the adhesive layer in direct contact with the wax skim coat.
An example of a “skim coat-containing” heat-transfer label assembly of the type described above is disclosed in U.S. Pat. No. 6,099,944, inventors Laprade et al., which issued Aug. 8, 2000, and which is incorporated herein by reference. According to the aforementioned patent, a label assembly is provided that is designed for use in decorating clear glass articles in such a way as to give such articles the appearance of having been frosted. In a preferred embodiment, the label includes (a) a support portion in the form of a sheet of paper overcoated with a release layer of polyethylene, (b) a skim coat of wax overcoated onto the polyethylene release layer and (c) a transfer portion, the transfer portion including a protective lacquer layer printed onto the skim coat, an ink layer printed onto the protective lacquer layer, and an adhesive layer printed onto the ink layer, as well as onto any exposed portions of the underlying protective lacquer layer and onto a surrounding area of the skim coat. The protective lacquer layer comprises a solvent-soluble phenoxy resin that has been cross-linked by a melamine resin. The ink layer comprises a design printed with a frosted ink, the frosted ink preferably comprising a solvent-soluble phenoxy resin, a silica and a colorant. The adhesive layer comprises a phenoxy resin of the type present in a water-based phenoxy resin dispersion.
Examples of other “skim coat-containing” heat-transfer label assemblies are disclosed in the following U.S. patents, all of which are incorporated herein by reference: U.S. Pat. No. 5,800,656, inventors Geurtsen et al., issued Sep. 1, 1998; U.S. Pat. No. 6,096,408, inventors Laprade et al., issued Aug. 1, 2000; U.S. Pat. No. 6,033,763, inventors Laprade et al., issued Mar. 7, 2000; and U.S. Pat. No. 6,083,620, inventors Laprade et al., issued Jul. 4, 2000.
When using a “skim coat-containing” heat-transfer label assembly of the type described above to decorate an article, one typically preheats the article and the label assembly prior to decoration. More specifically, where the article is made of glass, the article is typically preheated to a temperature of about 300° F. In addition, a silane adhesion promoter is also typically applied to the glass article prior to preheating. Decoration is typically performed by applying heat to the bottom of the carrier while the top of the label is pressed against the article. Once the transferred portion of the heat-transfer label assembly has been applied to the article, the labeled article is then typically subjected to a post-heating step so that the protective lacquer layer and/or the adhesive layer, one or both of which typically comprise thermosetting resins, may be cured. (By contrast, the ink layer of the above-described heat-transfer label assembly does not include a thermosetting resin.) Said post-heating step is typically performed by conveying the labeled articles through one or more industrial ovens to heat the articles to an elevated temperature, such as about 400° F. to about 425° F., for a particular amount of time, typically 15-20 minutes.
In certain instances, it may be desirable to re-use a container that has been labeled with a heat-transfer label. For example, it may be desirable, for environmental or financial reasons, for a labeled container holding a consumable item, such as a beverage or a health or beauty product, to be returned to the manufacturer of the consumable item after the consumable item has been consumed so that the container may be refilled with the consumable item and then re-sold. However, as can readily be appreciated, such a reusing of the labeled container requires that the labeled container be cleaned satisfactorily prior to being refilled with the consumable item. In many cases, particularly where the container is a glass container, such a cleaning typically involves a caustic wash conducted at elevated temperatures. One difficulty with cleaning the container in the aforementioned fashion, however, is that such a cleaning process typically causes chemical damage to the label as a result of the caustic wash. In addition, the label may also become damaged during washing and/or refilling through abrasion effects due to contact between two or more containers or between a container and the washing and/or filling equipment. Moreover, such chemical and/or abrasive damage may be exacerbated if the container is re-used not merely once but a number of times.
Therefore, there is a clear need for a heat-transfer label that can be applied to a container and that exhibits sufficient chemical and abrasion resistance to withstand one or more caustic washing and/or refilling cycles.